deppack: Tell the compiler not to make overly optimistic assumptions about stack alignment.

This prevents crashes when the built libraries use SSE instructions in certain ways.
deppack: Update to newest upstream versions of dependency libraries.

The patch to pkg-config is dropped because it has been applied upstream.

The patch to ffmpeg is modified to ignore installation errors on another file.
deppack: Add libpng.
deppack: Add libjpeg.
deppack: Add FLAC.

The patch is from upstream git and needed for modern MinGW toolchains.
deppack: Add freetype.
deppack: Add SDL_ttf.
deppack: Add SDL_image.
deppack: Add PortMidi.